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I want to make my own valve amplifier, and for that, I'll be using an 12AU7 dual triode tube. Since the 12AU7 is quite large, is there a sub-miniature version available?

Also: the main difference between the European ECC82 and the American 12AU7 is the heater voltage of either 6.3V or 12.6V. I heard they can be both wired to use both voltages, could someone please explain how?

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There is no significant difference between the ECC82 and the 12AU7 - it's just different nomenclature for the different markets. As for the heater voltage, the two heaters can be connected in series (12.6 V @ 150 mA) or parallel (6.3V @ 300 mA). Parallel is more common since most mains transformers for valve designs have a 6.3V secondary winding. I have no idea whether a sub-miniature version is available.

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There are probably subminiature tubes that will work, but submini's tend to have smaller maximum power dissipation and plate voltages. So you will likely need to re-engineer the circuit, or at least recalculate dissipation. I would suggest finding another medium-mu dual triode on ebay, look at the specs on http://pw1.netcom.com/~wa2ise/radios/penciltubes.html and see if it will work in your circuit. For example, the 6111 has low gain like the 12AU7, but dissipation and plate voltages are limited.

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I would not suggest to anyone to use subminiature tubes instead of highly available 12AU7 or ECC82 if you prefer (or E82ECC). Besides this tube is very, very good in hi-fi assemblies and you should not low anode voltage way below 250V, although i made guitar amp with 12V on it's anode.

If you're not familiar with voltage higher then 100, I strongly suggest to use ECC88, very nice (maybe better) double triode which runs beautifully at 90V. And yes, this tube has different heater characteristics (only parallel heaters).

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the 12AU7 and other 12A?7 derivatives can be run off a 12-Volt supply. try a google search on DIY headphone Hybrid amplifiers. in addition there are now Low voltage pencil tubes available out of the Former Soviet Union, some of these tubes have a maximum plate voltage of 30 volts, which are designed to be run off battery packs.

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